Absorber Layer In Solar Cells Research Articles

Morphological and Structural Characteristics of Sb2Se3 Thin Films Fabricated by Chemical Molecular Beam Deposition

This work presents the structural and morphological characteristics of antimony selenide (Sb2Se3) thin films, which were deposited by the chemical molecular beam deposition (CMBD) in atmospheric pressure hydrogen flow on an alkali glass substrate. It was found that the deposition temperature affected the morphology and structure of the films. At a low deposition temperature of 720 K, the film depicts a preferable crystal orientation (211), i.e., one-dimensional (1D) Sb2Se3 ribbons are aligned along the growth direction. Morphological studies show that the grain size increases with the temperature of the substrate; however, the 1D Sb2Se3 chains tend to align along the lateral direction. The Sb2Se3 films were found to have a preferable orientation (211) and polycrystalline structure. At higher substrate temperatures of 770 and 820 K, they also have a polycrystalline structure, but with an orientation (120). The studies of surface morphology show that at low substrate temperatures the samples have fine grains that have sizes of (200–300) nm, but are rather tightly packed and have 1D Sb2Se3 chains, which are aligned along the growth direction that corresponds to the orientation (211). It was found that the Sb2Se3 thin films with the orientation (211) were suitable for an absorber layer of solar cells, due to their anisotropic properties.

Effects of anti-solvent in the two-step fabrication of absorber layer in perovskite solar cells

Hybrid organic-inorganic perovskite materials, e.g., CH3NH3PbI3 (MAPbI3) have been used as photon absorber layer in the emerging solar cell technology. The two-step spin coating technique has been employed to fabricate the absorber films. It has been found that the use of anti-solvents plays a crucial role on the growth of the perovskite crystals. Chlorobenzene (CB) and Toluene (TO) were chosen as the anti-solvents that were applied after spin-coating of Methylammonium Iodide (MAI) solution in the second step of the two-step process. The amount and the elapsed time of the application of anti-solvents after spinning MAI solution were varied and studied for the crystal growth of perovskite films as well as the performance of the perovskite solar cells (PSCs). It was found that 50 ml of CB applied at 5 s after spinning MAI solution yielded the best solar cells parameters with the best efficiency of 16.8 %.

The role of copper during the growth of stoichiometric Cu2ZnSnS4 by successive ionic layer adsorption and reaction method

The synthesis and characterization of Cu2ZnSnS4 (CZTS) thin films prepared on glass/CdS substrates by the successive ionic layer adsorption and reaction (SILAR) method are presented. The effect of copper concentration and atmosphere annealing on the properties of CZTS thin films were studied by means X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM), X-ray photoelectron spectroscopy (XPS), optical spectroscopy and current-voltage curves. The XPS depth profiling data revealed that a minima copper concentration in cationic solution is required to start the adsorption of zinc and tin ions at the CdS surface. The use of 0.001–0.002 M copper concentration allows the adsorption of zinc and tin ions in a suitable quantity inducing the formation of stoichiometric and polycrystalline CZTS thin films. Furthermore, it was found that above of this copper concentration, the segregation of Cu2S phase occurs, even when it is ten times smaller than Zn and Sn concentrations. Otherwise, the sulfurization process doesn't imply a significant change on the structural and chemical properties, as if it does in the optical and electrical properties. This suggests that the excess of Na2S used in the anionic solution is enough to compensate the loss of sulfur during the thermal annealing. The optical band gap energy and the electrical conductivity of these films were evaluated in the range of 1.41–1.53 eV and 10−1 Ω cm−1, respectively. All results suggested that this material is suitable for being applied as an absorber layer in photovoltaic solar cells.

Deposition of Cu2ZnSnS4 films by doctor blade printing using a one-step microwave heated ink as an absorber layer for solar cells

Kesterite (Cu2ZnSnS4, CZTS) semiconductors are known as the most suitable compounds for the synthesis of absorber layers. These compounds are used in solar cells due to their high solar energy absorption coefficient and ideal band gap. In the present work, the microwave-assisted process and doctor blade printing were used to prepare Cu2ZnSnS4 films. To this aim, ink solution was used, which consisted of copper, zinc acetate, tin chloride and thiourea as copper, zinc, tin and sulfur precursors, respectively. Ethylene glycol was used as a non-toxic solvent. The CZTS ink was prepared using microwave heating for 10 min. The CZTS layers were printed on soda lime silica glass substrates and heat treated at 150, 200, 250, 300, and 350°C. The microstructure, phase analysis, morphology, optical properties, and absorption ratio of the samples were evaluated using X-ray diffraction analysis, Raman spectroscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, transmittance spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray, and UV–Vis spectrophotometry. The formation of the Kesterite structure was confirmed using X-ray diffraction and Raman spectroscopy. The FESEM micrographs and DLS (dynamic light scattering) revealed that the films contained equated grains with the diameter range of 350–650 nm. According to the X-ray analysis and Raman spectrum, the highest crystallization and purity of the Kesterite phase as well as the best microstructure property and morphology (smooth spherical particles with good adhesion) of the CZTS films were found in the synthesized specimen at 300°C. The band gap of the samples was measured to be about 1.5 eV using UV–Vis spectrophotometry.

Performance evaluation and material parameter perspective of eco-friendly highly efficient CsSnGeI3 perovskite solar cell

Abstract Lead toxicity and stability are major hurdles in commercialization of the perovskite solar cell. We present the theoretical investigation and analysis of eco-friendly and stable CsSnGeI3 based solar cell. For better understanding of material parameter, various factors affecting the cell performance such as thickness, doping concentration, defect density and doping density of charge transport layer have been rigorously investigated. From simulation results, we observed that the device performance extensively depends on defect density and doping concentration of perovskite absorber layer. We have proposed Cesium Tin–Germanium Tri-iodide (CsSnGeI3) as an efficient light absorber material as compared to lead counterparts. With optimized parameters of proposed architecture, we have achieved 13.29% efficiency. We have also done the comparative analysis of different hole transport layer (HTL) layers to replace spiro-OMeTAD. The results indicate that CsSnGeI3 can be a great prospective to be an absorber layer for high-efficiency perovskite solar cells.

Mechanism study of Zn/Sn ratio on the MoSe2 formation in Zn-rich Cu2ZnSnSe4 absorber layer

Controlling the thickness of the interfacial MoSe2 layer in Cu2ZnSnSe4 (CZTS) thin film solar cells can have a profound impact on device performance. The Zn/Sn ratio in the absorber layer of CZTS solar cells significantly affects the thickness of MoSe2 after selenization; however, the underlying mechanism remains unknown. In this study, we employed a fast-cooling selenization system to study the phase transformation and analyzed the back side of the CZTS absorber layer to characterize the mechanism by which Zn/Sn ratio affects the thickness of the MoSe2 absorber layer. Experiments revealed the formation of various metal-selenide phases at the bottom of the CZTS absorber layer during selenization. At temperatures below 400 °C, this mainly involves Sn- and CuSn-selenides; above 450 °C, this mainly involves Cu- and Zn- selenides. Since MoSe2 grows significantly above 450 °C, Cu- and Zn-selenides are the main reasons for reducing the thickness of MoSe2. The fact that MoSe2 growth generally occurs above 450 °C means that a higher Zn/Sn ratio leads to the formation of more Zn-selenides, such that there is less Se available for the formation of MoSe2, resulting in a thinner layer.

Substrate temperature dependent physical properties of SnS1−xSex thin films

Recently, researchers showed great interest on SnS1−xSex alloy films because of their tunable physical properties that are suitable as an absorber layer in thin film solar cells. In the present work, SnS1−xSex thin films were deposited by thermal co-evaporation of SnS and Se at different substrate temperatures ranging from 200 to 350 °C. The influence of substrate temperature (Ts) on composition, structure, surface morphology, topography and optical properties of as-deposited films was investigated using appropriate techniques and the results are reported in detail. The EDS analysis of SnS1−xSex films showed that Sn/(S + Se) ratio was changed from 0.84 to 1.16 with increase of substrate temperature. All the films were polycrystalline in nature, exhibiting (111) plane as preferred orientation with orthorhombic crystal structure. From W–H analysis, the crystallite size and lattice strain in the films were evaluated, where the crystallite size varied in the range, 9–22 nm with substrate temperature. The layers showed a change in the shape of grains with the rise of substrate temperature, where the grain size has increased with Ts. The topographical results indicated an indirect relation between surface roughness and average grain size with change in substrate temperature. The band gap energy values of the films was decreased with increase of Ts and varied in the range, 1.59–1.46 eV. In addition, the photoconductivity measurements revealed that the as-deposited SnS1−xSex films had bimolecular type recombination (γ ~ 0.5) of photo-generated charge carriers.

Efficiency Improvement of CZTSe Solar Cell with Ag Doped Zno/Cds Buffer Layer, using Scaps Simulation Programme

Compound semiconductor CZTSe is a popular absorber layer for thin film solar cells. Instead of single semiconductor buffer layer, a hybrid buffer layer is used with CZTSe absorber layer. To reduce further usage of toxic materials(CdS) and simultaneously to increase the solar cell efficiency, Ag doped buffer layer was proposed and a numerical studies were performed using SCAPS 1-D simulation programme. Also the thickness and the carrier density of the different layers in the solar cell were optimized to achieve the above goals. After the simulation process, the toxic materials usage was reduced by 62% and the efficiency was increased from 12.24% to 12.69%

Structural and optical properties of CZTS nanoparticles prepared by a colloidal process

This research presents the influence of copper (Cu) concentration on the properties of copper zinc tin sulfide (CZTS) nanoparticles (NPs) synthesized by a colloidal method, employing oleylamine as an organic solvent. From the structural analysis, a pure phase of CZTS was obtained at an optimized molar ratio of 1.8:1.1:1:4, and secondary phases were observed as the Cu concentration increased. The increment of the NPs size from 15 to 50 nm was noticed as a function of Cu concentration. Importantly, the optical bandgap energy was tuned from 1.35 to 1.68 eV with respect to Cu concentration. The sample synthesized at the molar ratio of 1.8:1.1:1:4 showed a pure phase CZTS with desired elemental composition and bandgap. Furthermore, CZTS thin films were prepared by a doctor-blade method using synthesized NPs followed by annealing under a sulfur/nitrogen atmosphere. The annealed CZTS film showed a significant improvement in the morphological, electrical and optoelectronic properties. Thus, the annealed CZTS film can be efficiently used as an absorber layer in low-cost thin film solar cells. Synthesis of CZTS nanoparticles by hot injection process at different copper concentration and their impact on the particle size & bandgap.

Temperature dependent growth of Cu2SnS3 thin films using ultrasonic spray pyrolysis for solar cell absorber layer and photocatalytic application

Ternary chalcogenide Cu2SnS3 (CTS) thin films are deposited on glass substrates using low cost ultrasonic spray pyrolysis (USP) technique by varying substrate temperatures 300 °C to 550 °C. Crystal structure of CTS thin film is found to change its phase from amorphous to tetragonal phase with increase in substrate temperature. Properties of as-deposited Cu2SnS3 thin films are studied using various characterization techniques. X-ray powder diffraction (XRD) studies confirm the formation of Cu2SnS3 tetragonal phase with orientation along (112) plane with increase in substrate temperature. Raman analysis revealed the formation of binary phase at 550 °C substrate temperature. Increase in substrate temperature resulted in stoichiometric nature of Cu2SnS3 films at 500 °C. The absorption coefficient of CTS films is found to be ∼105 cm−1 with band gap ranging from 1.35 eV to 1.48 eV. Electrical properties of CTS films exhibited p type conductivity with carrier concentration of the order of 1021 cm−3. The resistivity of the CTS films is found to vary from 1.5 × 10−3 to 3.2 × 10−3 Ω-cm. Photocatalytic effect of optimized Cu2SnS3 thin film under visible light (300 W) is examined with methylene blue (MB) dye and ∼90% MB is degraded under 3 hours visible light irradiation. The above properties indicate that Cu2SnS3 is a potential candidate to be used for solar cell absorber layer and photocatalytic activity.

Surface statistical properties of solid state reacted CZTSe compounds prepared in five different ratios

Copper Zinc Tin Selenide (CZTSe) has attracted much attention in recent times, for an absorber layer in thin film solar cells, due to high natural abundance of its constituents and their non-toxicity. In this work preparation of CZTSe compounds through solid state reaction of elemental precursors, namely Cu, Zn, Sn and Se and study of surface roughness, using the atomic force microscopy (AFM) has been presented. In order to study the influence of compositional variation on surface morphology, quantitative roughness and surface characteristics have been evaluated from AFM characterization. Surface roughness and grain size along with parameters like surface kurtosis, skewness and root mean square (RMS) roughness have been discussed. A significant difference has been observed in roughness parameters and grain size with respect to Cu/Zn variations. It has been concluded that deficiency of Cu and excess of Zn, caused decrement in mean grain size of the material with respect to perfect stoichiometric sample. These observations have also been verified using SEM-EDAX and FTIR studies.

A theoretical and experimental study of the valence-band electronic structure and optical constants of quaternary copper mercury tin sulfide, Cu2HgSnS4, a potential material for optoelectronics and solar cells

Experimental and theoretical studies on the electronic-band structure and optical constants are made for the first time for quaternary copper mercury tin sulfide, Cu2HgSnS4. The present X-ray photoelectron spectroscopy studies reveal low hygroscopicity of Cu2HgSnS4 alloy surface and its sensitivity to 3 keV Ar+-ion irradiation that decreases substantially the content of mercury atoms in topmost analyzing layers. Performed within density functional theory (DFT) the present band-structure calculations show that the best coincidence with the experiment is derived when the computational procedure is made employing for exchange correlation potential modified Becke-Johnson functional and also including Hubbard parameter U and spin-orbit coupling. The present DFT calculations indicate that S 3p states are the main contributors to the broad region of the valence band of Cu2HgSnS4 (in the central and upper portions of the band), while in its lower part contributions of Hg 6s and Sn 5s states prevail and Hg 5d states dominate at its bottom. A conduction band bottom is formed due to contributions of unoccupied Sn 5s states with also substantial input of unoccupied S 3p and Hg 6s states too. The DFT calculations allow for concluding that the Cu2HgSnS4 compound is a direct bandgap semiconductor with valence band maximum and conduction band minimum positioned at Г point. The calculations indicate that Cu2HgSnS4 is a very prospective material for application in optoelectronic devices and absorber layers of thin films solar cells.

Narrow band gap high conducting nc-Si1-xGex:H absorber layers for tandem structure nc-Si solar cells

Advantages of spectral sensitivity in the infrared range and good stability against light exposure together have made nanocrystalline silicon–germanium alloy (nc-Si1-xGex) as an ideal absorber material at the bottom-cell in multi-junction Si thin film solar cells. Evolution of good quality SiGe thin films with sustained nanocrystallinity, particularly at low growth temperature (TS), is a challenging task in view of very different chemical reaction behaviors controlled via different energy requirements of two frequently used source gases, e.g., SiH4 and GeH4. Growth of nc-SiGe:H thin films have been pursued at TS ∼220 °C, using H2-diluted (by ∼96%) (SiH4 + GeH4) plasma in 13.56 MHz RF-PECVD, by varying the RF power applied to the parallel plate capacitively coupled electrodes of the reactor. At lower RF power Ge-dominated low band gap SiGe network has been produced with Si component in mostly amorphous configuration that leads to a low electrical conductivity. At high RF power Si–Si network becomes highly crystalline; however, Ge content reduces drastically. Breaking of weaker Ge–Ge bonds creates defects via dangling bonds and increased grain boundary defects around Si nanocrystals together produce relatively wider band gap SiGe network with degraded electrical conductivity. The novelty and significance of the present investigation remains in realizing the narrowing of the optical band gap (Eg ∼1.499 eV) even at lower Ge content, through moderate crystallization in the SiGe network and a simultaneous high electrical conductivity of the nc-SiGe:H films (σD ∼2.38 × 10−3 S cm−1) obtained at a high growth rate (∼9.5 nm/min), via optimization of the applied RF power at a moderate level (∼100 W). In such circumstances nanocrystallization of the network plays leading role in narrowing the optical band gap, overriding the effect arising out of the restricted presence of Ge.

Efficiency Enhancement with the Ferroelectric Coupling Effect Using P(VDF-TrFE) in CH3NH3PbI3 Solar Cells.

A novel ferroelectric coupling photovoltaic effect is reported to enhance the open‐circuit voltage (V OC) and the efficiency of CH3NH3PbI3 perovskite solar cells. A theoretical analysis demonstrates that this ferroelectric coupling effect can effectively promote charge extraction as well as suppress combination loss for an increased minority carrier lifetime. In this study, a ferroelectric polymer P(VDF‐TrFE) is introduced to the absorber layer in solar cells with a proper cocrystalline process. Piezoresponse force microscopy (PFM) is used to confirm that the P(VDF‐TrFE):CH3NH3PbI3 mixed thin films possess ferroelectricity, while the pure CH3NH3PbI3 films have no obvious PFM response. Additionally, with the applied external bias voltages on the ferroelectric films, the devices begin to show tunable photovoltaic performance, as expected for the polarization in the poling process. Furthermore, it is shown that through the ferroelectric coupled effect, the efficiency of the CH3NH3PbI3‐based perovskite photovoltaic devices is enhanced by about 30%, from 13.4% to 17.3%. And the open‐circuit voltages (V OC) reach 1.17 from 1.08 V, which is reported to be among the highest V OCs for CH3NH3PbI3‐based devices. It should be noted in particular that the thickness of the layer is less than 160 nm, which can be regarded as semi‐transparent.

Preparation and characterization of Cu2CoSnS4 thin films for solar cells via co-electrodeposition technique: Effect of electrodeposition time

Quaternary compound Cu2CoSnS4 (CCTS) is a potential candidate absorber layer in thin film solar cells. In this work the Cu2CoSnS4 (CCTS) thin film was synthesized by co-electrodeposition of Cu-Co-Sn-S precursors on Molybdenum substrate, followed by a high temperature (500 °C) sulfurization under Argon atmosphere. The effect of the electrodeposition time of CCTS precursors (Cu, Sn, Co, S) on the crystallographic structure, morphology, composition and optical band gap of CCTS thin films was investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and energy dispersion spectroscopy. From the results, it was found that the properties of the sample can be improved by decreasing the deposition time and we have found that as the deposition time increases, the amount of the secondary phase Cu2-xS increases. The elemental composition is enriched in Co and S and depleted in Cu with increasing time. The band gap was determined from diffuse reflectance and found for all films in the range of 1.4–1.5 eV.

Effects of KF and RbF post deposition treatments on the growth of the CdS buffer layer on CIGS thin films - a comparative study

In this contribution we are analyzing and comparing the impact of two different alkali-fluorine post deposition treatments (KF and RbF) on the growth of chemical-bath-deposited CdS buffer layers on Cu(In,Ga)Se2 absorber layers for thin film solar cells. By combining Raman scattering, scanning electron microscopy, current-voltage analysis and measurements of the internal quantum efficiency we provide a comprehensive picture of this issue on the material and device level. We find that both PDTs lead to a better CdS-coverage of the surface of the CIGS, which leads to an improved junction quality at early growth stages compared to untreated devices. Furthermore the growth rate of the CdS is enhanced on KF-treated absorber layers while it is decreased on those treated with RbF (compared to the reference). This leads to a more stable behavior of RbF-treated devices after longer duration of the CdS deposition, while the KF-treated devices suffer from reduced fill factor and open circuit voltage. Furthermore we show that not only both PDTs but also the growth of the CdS lead to a reduction of the amount of the so called ordered defect compound, which is initially present at the surface of our absorber layers. This behavior indicates either the formation of CdCu -anti-sites or of a secondary phase at the interface.

CuZnInSe3‐based solar cells: Impact of copper concentration on vibrational and structural properties and device performance

AbstractCuZnInSe3 (CZISe) is an interesting alternative for the acknowledged Cu(In,Ga)Se2 absorber layer in thin film solar cells. While the partial replacement of scarce and expensive indium and gallium by zinc decreases manufacturing costs, the solid solution between CuInSe2 and ZnSe opens interesting options for band gap tuning and grading. Its potential as an absorber layer in photovoltaic devices has been demonstrated by obtaining 7.4 and 7.6 % efficiency in CZISSe‐ and CZISe‐based devices, respectively. On the other hand, the inherent complexity of the quaternary CZISe together with a lack of fundamental insights puts a limit to its current development. We present insights on the influence of the copper content ([Cu]/([Zn] + [In]) ratio) on the structural and optoelectronic properties of CZISe as well as the formation of secondary phases. By means of XRD and Raman scattering analyses, in addition to the sphalerite CZISe structure, a chalcopyrite Cu‐In‐Zn‐Se phase was found for high copper concentrations. On the contrary, for low Cu concentrations, unambiguous indications of a new ordered vacancy compound (OVC)–like phase formation both in XRD patterns and in Raman spectra were found. Conditions of pre‐resonant Raman scattering were applied to emphasize the new found phase and to estimate its concentration. Finally, the influence of each phase on the optoelectronic parameters and performance of solar cells with efficiencies of up to 7.4 % was studied.

Synthesis and characterization of Cu2CoSnS4 thin film via electrodeposition technique for solar cells

Quaternary compound Cu2CoSnS4 (CCTS) is a potential candidate absorber layer in thin film solar cells to produce clean and inexhaustible energy. In this work the Cu2CoSnS4 (CCTS) thin film was synthesized for the first time by co-electrodeposition of Cu–Co–Sn–S precursors on Molybdenum substrate, followed by a high temperature (500 °C) sulfurization under Argon atmosphere. The potential deposition (−0.95 V/SCE) was determined from cyclic voltammetry . The structure, composition and morphology of the CCTS thin film is characterized in detail by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and energy dispersion spectroscopy. The p-type conductivity of CCTS thin film was confirmed using Mott–Schottky analysis and the band gap value was evaluated to be 1.56 eV, which makes CCTS a promising material for solar cell applications.

Role of soaking time on the phase evolution of Cu2ZnSnS4 polycrystals synthesized using melting route for photovoltaic applications

Cu2ZnSnS4(CZTS) is an emerging quaternary semiconductor material to use as absorber layer for solar cells due its suitable band gap, high absorption coefficient, earth abundancy and less toxic nature. This work provides a comprehensive insight into the phase evolution of CZTS synthesized at a relatively lower process time. In this study, CZTS bulk polycrystals were synthesized using elemental pre cursors via melting route. The influence of soaking time on the structural, compositional and optical properties were investigated using XRD, EDS, Raman, DRS, PL and XPS measurements. XRD pattern revealed a highly crystalline tetragonal structure corresponding to kesterite phase. EDS mapping were performed over a large area of the sample revealed homogeneous distribution and near stoichiometric composition for the sample soaked for 14 h (S14). Raman spectra confirmed the existence of single phase CZTS without any secondary and ternary phases for S14. Diffuse reflectance spectroscopy gave a band gap value in the range 1.34–1.39 eV. PL analysis revealed that asymmetric band shape and higher energy shift is the characteristics of radiative transitions which are influenced by fluctuating potentials. XPS studies confirmed the oxidation states as Cu(I), Zn(II), Sn(IV) and S(II).

Characterization of Cuprous Oxide Thin Films for Application in Solar Cells

Cuprous oxide (Cu2O) has a high optical absorption coefficient and favourable electrical properties, which make Cu2O thin films attractive for photovoltaic applications. Using reactive radio-frequency magnetron sputtering, high quality Cu2O thin films with good carrier transport properties were prepared. This paper presents the characteristics of Cu2O thin films that were sputter deposited on quartz substrates and subjected to post-deposition rapid thermal annealing. The thickness of the thin films and the optical constants were determined by ellipsometry spectroscopy (SE). The optical transmittance increased in lower wavelength region after annealing at 900 ̊C in rapid thermal annealing (RTA). The structural and morphological properties of the Cu2O thin films were investigated by electronic scanning microscopy (SEM) and atomic force microscopy (AFM), whereas elemental analysis was performed by X-ray fluorescence spectroscopy (XRF). The carrier mobility, carrier density and film resistivity were changed after post-deposition rapid thermal annealing from respectively ~14 cm2/Vs, ~2.3 x 1015 cm-3 and ~193 Ωcm for the as-deposited Cu2O film to ~49 cm2/Vs, ~5.0 x 1014 cm-3 and ~218 Ωcm for the annealed Cu2O film. The investigation suggests that the sputter-deposited Cu2O thin films have good potential for application as absorber layers in solar cells.